Method and System for Correcting an Optical Beam

ABSTRACT

Embodiments of the present invention provide a system and method for shaping an annular focal spot pattern to allow for more efficient optical coupling to a small gauge optical fiber. An embodiment of the present invention can include an illumination source operable to transmit an optical beam along an optical path, an optical fiber, and a correcting element positioned in the optical path between the illumination source and the optical fiber, the correcting element configured to reshape the optical beam to increase an amount of light received by the optical fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Patent Application No. 60/787,969, filed Mar. 31, 2006, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of illuminationsystems. In particular, the present invention relates to ophthalmicillumination systems and, more particularly, to a method and system forprismatic correction of an optical beam in an ophthalmic illuminationsystem to improve coupling of the optical beam to a small diameteroptical fiber.

BACKGROUND OF THE INVENTION

Many ophthalmic surgical procedures require illuminating a portion of apatient's eye so that a surgeon can observe the surgical site. Variousdifferent types of instruments are known and available for use by anophthalmic surgeon to illuminate the interior of the eye. The handheld(probe) portion of a typical ophthalmic illuminator comprises a handlehaving a projecting tip and a length of optical fiber that enters aproximal end of the handle and passes through the handle and the tip toa distal end of the tip, from which light traveling along the opticalfiber can project. The proximal end of the optical fiber can bepositioned adjacent to a light source, such as in a high brightnessilluminator, as known to those having skill in the art, to provide thelight that is transmitted through the fiber. These types of handheldilluminators are typically used by inserting the probe tip through asmall incision in the eye. In this way, light from the illuminator lightsource is carried along the optical fiber, through the handpiece andemitted from the distal end of the probe (fiber) to illuminate thesurgical site for the surgeon. Ophthalmic illuminators that use a lengthof optical fiber to carry and direct light from a light source to asurgical site are well known in the art.

Such an ophthalmic illumination system typically comprises a handheldportion, or probe, to deliver illumination from a light source housed inan enclosure, the enclosure typically housing the light source andassociated optics that guide light from the light source to the opticalfiber of the probe, a power supply, electronics with signal processing,and associated connectors, displays and other interfaces as known in theart. While some ophthalmic illumination systems use other types of lampsas a light source, a preferred light source is a xenon lamp. Some priorart xenon lamps exists that use quartz for the lamp body material.However, quartz has been found to be unstable at the high operatingtemperature of typical xenon lamps and has a tendency to fail andsometimes explode. This is because as the quartz lamp body ages, thequartz crystallizes, cracks, and is then susceptible to failure. As aresult, these prior art xenon lamp illuminators contain the xenon lampand quartz lamp body within a steel housing. Ceramic lamp bodies, on theother hand, have been found safe for use in the high temperatureenvironment of a xenon lamp. Most modern ophthalmic illumination systemsusing xenon lamps thus typically employ a ceramic body.

However, unlike with a quartz lamp body, the electrodes of aceramic-bodied xenon lamp typically intrude into the lamp's opticalpath. This disadvantage is not present in prior art quartz-bodied lampsbecause the lamp electrodes are vertical and do not invade into theoptical path. However, in a ceramic body, the electrodes are placed suchthat they interfere with the center portion of the lamp's optical beam,resulting in a “donut” shaped optical beam instead of a more homogenous“dot-shaped” beam. The reflector, electrodes and their associatedsupports cast shadows within the optical beam resulting in a focal spothaving a donut shape, as shown in FIG. 1.

The annular-shaped focal spot of ceramic-bodied high-pressure xenonlamps has until recently not been a problem for ophthalmic illuminationsystems because these prior art systems typically use fiber bundles(e.g., 3 to 6 mm fiber bundles) to receive the annular focal spot andtransmit the received light from the light source to a surgical site.However, with the advent of small core-diameter optical fibers (e.g.,about 3 mm diameter) such as can be used with the Alcon High BrightnessIlluminator, manufactured by Alcon Laboratories, Inc., of Irvine,Calif., for use in ophthalmic endo-illumination systems, the annularfocal spot of prior art xenon lamps is in conflict with the desire tocouple the xenon lamp output into a small core optical fiber. This isparticularly so because these modern endo-illuminators typically use asingle fiber to guide and direct light from the light source to thesurgical site. Such small core optical fiber endo-illuminators aredesirable because they require a smaller incision and thus lessen traumaand possible damage to a patient's eye.

Focusing the output from a xenon light source in these prior artophthalmic illumination systems into a small core diameter optical fiberis thus not only difficult, but results in a poor optical-coupling tothe optical fiber. Further, the annular focal spot from such anilluminator is typically approximately 1 mm in diameter. Focusing thisannular focal spot into an approximately half a millimeter fiber (e.g.,a typical 25-gauge optical fiber) results in an irregular intensitydistribution of the transmitted light. Note that for a 20 gauge opticalfiber the problem is not as great because the entire annular focal spotcan fit within the 20-gauge optical fiber diameter.

Prior art ophthalmic illumination systems have attempted to solve thisproblem by defocusing the annular focal spot to direct some light intothe central portion of the focal spot. The problem with this approach isthat as the focal spot is defocused, the intensity of the transmittedlight decreases because less of the light from the light source isdirected into the optical fibers. Further, although prior art ophthalmicillumination systems do not focus the output of the xenon lamp into asingle optical fiber, when focusing the output of the xenon lamp into afiber bundle, prior art illuminators have attempted to beam-shape theoutput of the xenon lamp by the use of diffractive optical elements. Theproblem with the use of diffractive elements is that they are sensitiveto changes in the light source beam, and the output from a xenon lampchanges significantly as the lamp ages. Also, inexpensive custom-madediffractive elements are typically made of plastic, which can be damagedrelatively easily by a high intensity optical beam originating at axenon lamp.

Therefore, a need exists for a method and system for correcting anoptical beam that can shape the annular focal spot pattern from a highpressure ceramic xenon lamp into a focal spot with quasi-Gaussianintensity distribution for efficient optical fiber coupling. Furtherstill, there is a need for such a method and system for correcting anoptical beam that will provide stable correction as a lamp source agesand that can improve fiber coupling efficiency of the lamp source outputinto a small (e.g., ≦3 mm diameter) optical fiber, such as 20 and 25gauge optical fibers.

BRIEF SUMMARY OF THE INVENTION

The embodiments of the method and system for correcting an optical beamof the present invention substantially meet these needs and others. Oneembodiment of the system for correcting an optical beam of thisinvention comprises: an illumination source operable to transmit anoptical beam along an optical path, an optical fiber and a correctingelement positioned in the optical path between the illumination sourceand the optical fiber, the correcting element configured to reshape theoptical beam to increase an amount of light received by the opticalfiber. The correcting element may reshape the optical beam from havingan annular focal spot to having a focal spot with a more Gaussianintensity distribution than the annular focal spot.

Other embodiments of the present invention can include a method forcorrecting an optical beam in accordance with the teachings of thisinvention. One embodiment of the method comprises: generating an opticalbeam using an illumination source, directing the optical beam to acorrecting element, reshaping the optical beam using the correctingelement to have a focal spot with a more Gaussian intensity distributionthan prior to the correcting element, optically coupling the shapedoptical beam to an optical fiber and directing the optical beam to asurgical site.

Another embodiment of the present invention can comprise an opticalcorrecting system for a high-pressure xenon lamp illuminator opticalcoupling comprising: an illumination source, a first mirror opticallycoupled to the illumination source to receive an optical beam from theillumination source, a second mirror optically coupled to the firstmirror to receive the optical beam from the first mirror, a firstcorrecting element in optical communication with the illuminationsource, wherein the first correcting element reshapes the optical beamto have a focal spot with a more Gaussian intensity distribution thanupstream of the correcting element and a first optical fiber port inoptical communication with the first correcting element and operable tobe coupled to the proximal end of an optical fiber.

Embodiments of this invention can be implemented within a surgicalmachine or system for use in ophthalmic or other surgery. In particular,it is contemplated that the method and system for correcting an opticalbeam of this invention can be implemented in, or incorporated into, anyophthalmic illumination system in which it is desirable to efficientlycouple a xenon light source optical beam to a small diameter opticalfiber. Other uses for the method and system for correcting prismatic anoptical beam in accordance with the teachings of this invention will beapparent to those having skill in the art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription, taken in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features and wherein:

FIGS. 1 and 2A show a typical focal spot intensity distribution of anoptical beam from a high output ceramic-bodied xenon lamp;

FIG. 2B shows a preferred Gaussian focal spot intensity distribution ascan be achieved using embodiments of the present invention;

FIG. 3 is a simplified block diagram of a high-brightness ophthalmicillumination system incorporating an embodiment of the optical elementfor correcting an optical beam of the present invention;

FIG. 4 shows a high brightness ophthalmic illumination systemincorporating another embodiment of the present invention comprising asingle correcting element 22 upstream of hot mirror 18, instead of thedual correcting elements 22 of FIG. 3;

FIG. 5 is a diagrammatic representation illustrating the concept forbeam shaping of optical beam 28 in accordance with the embodiments ofthe present invention;

FIG. 6 is a diagrammatic representation of one embodiment of acorrecting element 22 of this invention that comprises a single zonenegative axicon 50;

FIG. 7 is a diagrammatic representation of one embodiment of acorrecting element 22 of this invention that comprises a multi-zoneaxicon 52;

FIG. 8 is a graph of the coupled power vs. focal length for both 25gauge and 20 gauge fibers in one experiment conducted according to theteachings of this invention;

FIG. 9 is an illustration of the area-solid angle product for an opticalfiber;

FIG. 10 is a graph showing coupled power vs. fiber numerical aperturefor a baseline coupling lens design focal length (0.866″) and for afocal length equal to 0.73″;

FIG. 11 shows a cross-section of one best performing axiconic designcorrecting element according to the present invention; and

FIG. 12 is a diagrammatic representation of a seven-zone Fresnel lensembodiment of correcting element 22 of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in theFIGUREs, like numerals being used to refer to like and correspondingparts of the various drawings.

The various embodiments of the method and system for prismaticcorrection of an optical beam of this invention provide for correctingthe annular focal spot pattern of a high-pressure xenon lamp for moreefficient optical coupling to a small gauge optical fiber. Theembodiments of this invention can reshape the optical beam profile totransform the annular focal spot into a more bell shaped (Gaussian)intensity distribution that will more efficiently couple the output ofthe xenon lamp into a small diameter optical fiber.

As can be seen in FIGS. 1 and 2A, the typical focal spot intensitydistribution of an optical beam from a high output ceramic-bodied xenonlamp is uneven, with its greatest intensity toward the edges of theoptical beam and lesser intensity toward the center. This intensitydistribution is inefficient for directing (coupling) a homogenous lightbeam to a small diameter optical fiber in, for example, anendo-illuminator probe, and will result in a light output from theendo-illuminator probe that is brighter along the edges and dimmer inthe center, which is not the preferred distribution for illuminating asurgical site. It is preferable to have a uniform intensitydistribution, or at least a distribution such as in FIG. 2B that is moreGaussian in nature with greater intensity in the center and intensitydecreasing outward toward the edges of the beam. The various embodimentsof the present invention can reshape the intensity distribution of anoptical beam in an ophthalmic illuminator from a distribution such as inFIG. 2A, to a distribution more closely related to that of FIG. 2B byproviding an optical correcting element (e.g., a prismatic correctingelement) in the optical path from the light source upstream of theendo-illuminator probe optical fiber proximal end. Further, the variousembodiments of the present invention provide a method and system forcorrecting an optical beam that, unlike the prior art, can provide astable, consistent optical beam output as the xenon illumination sourceages.

FIG. 3 is a simplified block diagram of a high-brightness ophthalmicillumination system incorporating an embodiment of the optical elementfor correcting an optical beam of the present invention. Illuminatorsystem 10 comprises power supply 12 and illumination source 14, coldmirror 16, a hot mirror 18, a beam splitter 20, mirror or beam splitter21, optical fiber ports 24 and correcting elements 22. Illuminatorsystem 10 can also include optical beam attenuators, such as thosedisclosed in pending U.S. application Ser. No. 11/204,305, which ishereby incorporated by reference in its entirety, for attenuating theoptical beam from illumination source 14. Illuminator system 10 also cantypically comprise one or more optical fiber probes 26, which comprisethe handheld portion of the illuminator system 10, including opticalfiber 34, which is optically coupled to the illumination source 14within enclosure 11. High-brightness illumination system 10 is exemplaryonly and is not intended to limit the scope of the present invention inany way. The embodiments of the present invention can be used in anysuch ophthalmic high-brightness illuminator or in any system or machinein which it is desirable to efficiently couple the output of a xenonlight source to a small gauge optical fiber.

Optical source 14 of illuminator system 10 comprises a xenon lamp asknown to those having skill in the art. Xenon lamp 14 emits light beam28, which is directed along the optical path comprising cold mirror 16,hot mirror 18, beam splitter 20, beam splitter 21, correcting elements22 and optical fiber ports 24. In an embodiment including beam splitter21, beam splitter 20 can be a 50/50 beam splitter and beam splitter 21can be a 98/2 percent beam splitter. Cold mirror 16 and hot mirror 18combine to remove the infrared components of light beams 28 (heat) andprovide a “cool” visible light beam 28 to the downstream opticalcomponents, as will be known to those having skill in the art.Correcting elements 22 reshape optical beam 28 in the manner disclosedherein. Each correcting element 22 can be custom designed for itsrespective optical path and the two need not be identical, though theycan be.

Although high-brightness illuminator system 10 is shown comprising twooptical fiber ports 24, it will be obvious to those familiar with theart that a single optical fiber port 24 or multiple optical fiber ports24 can be implemented within such a fiber optic illuminator system. Inone embodiment, dual optical fiber ports 24 can comprise a 25 gaugeoptical fiber port and a 20 gauge optical fiber port. Illuminator system10 further comprises a printed circuit board (“PCB”) 30, or itselectronic equivalent, to provide signal processing and controlfunctions. PCB 30 can be implemented in any manner and configurationcapable for performing the desired processing and control functionsdescribed herein, as will be apparent to those having skill in the art.Optical fiber ports 24 comprise a receptacle to receive the proximal endof an optical fiber probe 26 and its optical fiber 34, which areinserted into the high-brightness illuminator enclosure 11 and opticallycoupled to illumination source 14 to receive and direct light fromillumination source 14 onto a desired site. Optical fiber ports 24 canfurther comprise coupling lenses 29, which can be Melles Griot LAG ØØ5coupling lenses or similar aspherical coupling lenses for focusing lightbeam 28 onto the proximal end of optical fiber 34, as will be known tothose having skill in the art.

The embodiments of the present invention provide a correcting element 22upstream in the optical path before coupling lenses 29 in order totransform the annular focal spot from the xenon lamp into a Gaussianintensity profile focal spot. Correcting elements 22 provide beamshaping of light beam 28 and can in some embodiments comprise abeam-shaping module. Correcting element 22 can be an axiconic,isomorphic, or diffractive element, as will be known to those havingskill in the art. Correcting element 22 can also comprise a Fresnellens. Embodiments of the system for correcting an optical beam of thisinvention can comprise any such optical device that can be used to shapean annular focal spot into a focal spot having a more Gaussian intensitydistribution as described herein. FIG. 4 shows another embodiment ofsuch a system according to the present invention having a singlecorrecting element 22 upstream of hot mirror 18, instead of the dualcorrecting elements 22 of FIG. 3. The embodiment of FIG. 4 is a lowercost alternative having almost the same performance characteristics as adual correcting element 22 embodiment.

FIG. 5 is a diagrammatic representation illustrating the concept forbeam shaping of optical beam 28 in accordance with the embodiments ofthe present invention. Xenon light source 14 provides optical beam 28,which is directed into a beam shaper module 32 that transforms opticalbeam 28 in a manner as described herein. Reshaped optical beam 28 isprovided to coupling lens 29, which focuses the reshaped beam 28 onto anoptical fiber, such as optical fiber 34. The output from coupling lens29, as shown in the blow-up 33, is transformed by beam shaper module 32in combination with coupling lens 29 from an annular focal spot 35 to amore Gaussian focal spot 37.

FIG. 6 is a diagrammatic representation of one embodiment of acorrecting element 22 that comprises a single zone negative axicon 50.An alternative embodiment is shown in FIG. 7 and comprises a multi-zoneaxicon 52. Both devices introduce prismatic correction to an opticalbeam 28 that shifts the optical beam from an annulus towards the annuluscenter. Because an axicon correcting element 22 is a figure of rotationof a regular prism, the prismatic angular is applied in a circularfashion, shifting all points on the annulus towards the center. Amulti-zone axicon 52 provides better compensation since the optimalprismatic angle decreases with the distance of the beam from the centerin the collimated xenon lamp output.

The embodiments of correcting element 22 shown in FIGS. 6 and 7illustrate one set of angles for efficiently coupling the light outputfrom the xenon lamp 14 into a narrow gauge optical fiber such as opticalfiber 34. Using these axiconic elements with an ophthalmic illuminationsystem such as that of FIGS. 3 and 4, improvements in coupling theoutput from xenon lamp 14 into an optical fiber 34 were calculated usingan Advanced Systems Analysis (“ASAP”) optical software model. Theresults are shown in Table 1 below. TABLE 1 OPTICAL FIBER CAUGE 20 GFIBER 25 G FIBER Lamp age 450 HRS 50 HRS 450 HRS 50 HRS % vs % vs % vs %vs Output Units Im PS Im PS IM PS Im PS Lamp only 24 −4.0% 56 124.0% 8.440.0% 20 233.3% Lamp and Fresnel lens 37.4 59.6% 57 128.0% 13.8 130.0%21 250.0% Lamp and Axiconic lens 31.5 26.0% 53 112.0% 11.6 93.3% 20233.3%ASAP optical software predictions of fiber coupling efficiency withsingle and multi-zone axicons.

As can be seen from Table 1, a considerable advantage is achieved forthe case of an aged xenon lamp, assuring that the typical exponentialdecline of a Xenon lamp due to aging will be considerably slowed fromthat of ophthalmic illuminators in the prior art. This is an extremelydesirable result that allows extending Xenon lamp life in ahigh-brightness illumination system such as the Alcon High-BrightnessIlluminator manufactured by Alcon Laboratories, Inc. of Irvine, Calif.

In a typical ophthalmic illumination system 10 only a small fraction ofthe xenon lamp 14 output is coupled into the small gauge optical fibersof the endo-illuminator probe 26. This is because light from the xenonlamp 14 is typically lost in one of two places: (1) the xenon lamp is aspot light that illuminates the interior of the ophthalmic illuminationsystem enclosure and not just the coupling lenses; and (2) conservationof energy and radiance limit how much light can be forced into anoptical fiber.

In one experiment, the power coupled into a narrow gauge optical fiber,such as a 20 gauge or 25 gauge optical fiber, was calculated andrepeated for ten different coupling lens 29 focal lengths. FIG. 8 showsa graph of the coupled power vs. focal length for both 25 gauge and 20gauge fibers resulting from this experiment. As can be seen from FIG. 8,only a small fraction of the lamp output is coupled into the opticalfibers. As an example, in the system of FIGS. 3 and 4, the coupling lens29 directly downstream of the 50/50 beam splitter receives, in oneexperiment, 105 lumens while the lens directly downstream of the 98/2%beam splitter received 71 lumens. Conservation of energy and radiancedictate that, referring also to FIG. 9:A _(lens)Ω_(lens) =A _(fiber)Ω_(fiber), where Ω=2n(1−cos θ)   Eq. 1

Using a 20 G optical fiber as an example, the optical fiber is the limitwith an area-solid angle product equal to 5.6E−4 in²−sr. Light incidenton the optical fiber that exceeds this value will not couple into theoptical fiber. With a 0.84 inch diameter coupling lens 29, of the lightincident on the coupling lens 29 only the light within a 1 degree halfangle will couple into the optical fiber. Unfortunately, the xenon lampsubtends a 1.95 degree half angle as seen from the coupling lens. Thelamp output for a 1.95 degree half angle is 149 lumens while the lampoutput for a half angle equal to 1 degree is 42 lumens. Therefore, onlya fraction (42/149=0.282) or 30 lumens of the 105 lumens incident on thecoupling lens 29 will couple into the 20 G fiber.

Since the fiber numerical aperture ultimately limits the cone of lightcoupled into an optical fiber and since an extremely small f-number isunrealistic, one alternative is to decrease the coupling lens 29 focallength to 0.73″ in an effort to match the lens f-number and the fiberacceptance cone. FIG. 10 shows coupled power vs. fiber numericalaperture for the baseline design focal length (0.866″) and for a focallength equal to 0.73″.

Results when adding a Fresnel lens and an axiconic lens downstream ofthe xenon lamp are shown in Table 2. For this phase the Fresnel lens hasa series of cone shaped segments. We chose a Fresnel lens diameter equalto 1.25″ with a total of 6 zones. Table 2 shows the lamp 1 output powerincident on the 6 zones. TABLE 2 Lamp 1 output power vs. Fresnel zone.Zone Power Number (lumens) 1 149 2 315 3 286 4 112 5 21 6 6

Not only docs the lamp output power vary with zone number, the angulardistribution does also. The smaller the angular distribution the bettercoupling we will get into the fiber. To narrow lamp 1 angulardistribution we adjusted the tilt angles individually for each Fresnelzone facet. In fact, we calculated the power coupled into the 20 G fiberas a function of Fresnel zone facet angle for all six zones (Table 3).TABLE 3 Coupled power per Fresnel zone vs. facet tilt angle. FresnelFacet Tilt Angle Coupled Power (deg) (lumens) −12 1.5 −9 3.5 −6 2.6 −31.0 ZONE 1 0 0.2 3 0.1 6 0.1 9 0.1 12 0.2 −12 0.6 −9 5.0 −6 12.0 −3 9.6ZONE 2 0 5.8 3 2.7 6 0.7 9 0.0 12 0.1 −4 14.1 −3 16.0 −2 15.5 −1 13.6ZONE 3 0 12.0 1 10.2 2 8.8 3 7.4 4 5.9 −2 3.7 −1.5 4.2 −1 4.4 −0.5 4.4ZONE 4 0 4.6 0.5 4.7 1 4.8 1.5 4.5 2 4.4 −20 0 −15 0 −10 0 −5 0 ZONE 5 00 5 0 10 0 15 0 20 0 −20 0 −15 0 −10 0 −5 0 ZONE 6 0 0 5 0 10 0 15 0 200

Next we constructed a six zone Fresnel lens with the optimized facetangles from Table 3. The Fresnel lens increased the lamp 1 coupling from24 lumens to 37.4 lumens for the 20 G fiber, but had essentially noimpact on lamp 2 coupling for the 20 G fiber. Therefore, with theFresnel lens in place there is less difference in coupling between thenew and aged lamps.

An axiconic is governed by six independent parameters: two coordinatesfor a point on the surface, two coordinates for the first conic focus,and two coordinates for the second conic focus. To determine whether ornot an axiconic placed in front of a xenon lamp will improve coupling,we selected a point on the surfaces and then explored all combinationsof 5 values for each of the remaining 4 independent axionic variable. Intotal we calculated coupling for 625 different axiconic solutions. FIG.10 shows the family of axiconic surfaces that were explored. FIG. 11shows a cross-section of one best performing axiconic design. Theaxiconic lens increased the lamp 1 coupling from 24 lumens to 31.5lumens for the 20 G fiber and only slightly degrades lamp 2 coupling.

A parametric study vs. coupling lens focal length for a xenon lamp wasalso performed. The parametric study indicated that shorter focallengths can theoretically improve coupling by up to 75%. In practice,aberrations and diffraction are likely to limit improvement. Next, weshortened the coupling lens focal length to 0.73″ and then designed andadded a Fresnel lens and then an axiconic lens in front of the xenonlamp. Table 4 summarizes the results. The Fresnel lens is the bestperformer. The Fresnel lens narrows the angular output of the sourcecausing a larger fraction of the source power to strike the couplinglens within the angular subtense of the fiber. It may be possible toextend this angular preconditioning approach and increase coupling byadding a “pillow lens” structure (as seen on the tail-lamp of a car) tothe flat side of the Fresnel lens. Note however, that with each couplingimprovement the design becomes more sensitive to fabrication errors andchanges in the lamp distribution with time. TABLE 4 Coupling Power(lumens) 20 G fiber 20 G fiber 25 G fiber 25 G fiber Lamp 1 Lamp 2 Lamp1 Lamp 2 (Likely (Likely (Likely (Likely aged) 50 hr) aged) 50 hr) LampOnly 24 56 8.4 20 Lamp and Fresnel Lems 37.4 57 13.8 21 Lamp andaxiconic lens 31.5 53 11.6 20

As can be seen from the examples provided herein, one preferredembodiment of correcting element 22 is a seven-zone Fresnel lensoptimized for maximum coupling into a 25 gauge fiber, but otherembodiments can comprise a 6, 7 or 8 zone Fresnel lens for coupling intoa 20 gauge or 25 gauge fiber. In a preferred embodiment, a correctingelement 22 can be positioned in each optical path leading to each port24. An alternative embodiment can be a single correcting element 22embodiment as shown in FIG. 4, in which a correcting element 22 isplaced in the optical path before the 50/50 beam splitter and downstreamfrom the hot mirror 18. Further, an embodiment of the present inventioncan comprise two correcting elements 22, as shown in FIG. 3, in whicheach correcting element 22 is custom fit to its optical path. This is tocompensate, for example, for the fact that the beam splitters may not becompletely symmetrical and could result in some slight changes to theoptical beam 28 along each path. An embodiment in which correctingelements 22 are custom-fit can correct for such differences and othersimilar path-induced differences.

FIG. 12 is a diagrammatic representation of a seven-zone Fresnel lensembodiment of correcting element 22, along with the accompanying tiltangles for each of the varying zones.

Various embodiments of the present invention thus provide for improvedoptical coupling of a xenon light source beam to a small gauge opticalfiber. In particular, the embodiment of this invention can increasecoupling efficiency into 20 and 25 gauge or smaller optical fibers.Further, the embodiments of this invention provide the ability tosignificantly reduce the decay in coupling efficiency with time as axenon light source ages. Coupling efficiency and coupling stability overtime are improved, and the central shadowing resulting from an annularfocal spot of the prior art is reduced or eliminated. The embodiments ofthe present invention can be incorporated into any xenon lamp basedoptical device, such as an ophthalmic illuminator, where opticalcoupling of a light beam into a small gauge optical fiber is desired.

The present invention has been described by reference to certainpreferred embodiments; however, it should be understood that it may beembodied in other specific forms or variations thereof without departingfrom its spirit or essential characteristics. The embodiments describedabove are therefore considered to be illustrative in all respects andnot restrictive, the scope of the invention being indicated by theappended claims.

1. A surgical illumination apparatus, comprising: an illumination sourceoperable to transmit an optical beam along an optical path; an opticalfiber; and a correcting element positioned in the optical path betweenthe illumination source and the optical fiber, the correcting elementconfigured to reshape the optical beam to increase an amount of lightreceived by the optical fiber.
 2. The surgical illumination apparatus ofclaim 1, wherein the correcting element is configured to reshape theoptical beam from having an annular focal spot to having a focal spotwith a more Gaussian intensity distribution than the annular focal spot.3. The surgical illumination apparatus of claim 2, wherein thecorrecting element comprises an axiconic lens.
 4. The surgicalillumination apparatus of claim 3, wherein the axiconic lens comprises asingle-zone axicon.
 5. The surgical illumination apparatus of claim 3,wherein the axiconic lens comprises a multi-zone axicon.
 6. The surgicalillumination apparatus of claim 3, wherein the axiconic lens comprises anegative axicon.
 7. The surgical illumination apparatus of claim 3,wherein the illumination source comprises a xenon lamp.
 8. The surgicalillumination apparatus of claim 3, wherein the optical fiber has adiameter that is less than or equal to the diameter of a 25-gauge fiber.9. The surgical illumination apparatus of claim 1, wherein thecorrecting element comprises a fresnel lens.
 10. A surgical illuminationapparatus, comprising: an illumination source; a first mirror opticallycoupled to the illumination source to receive an optical beam from theillumination source; a second mirror optically coupled to the firstmirror to receive the optical beam from the first mirror; a firstcorrecting element in optical communication with the illuminationsource, wherein the first correcting element reshapes the optical beamto have a focal spot with a more Gaussian intensity distribution thanupstream of the correcting element; and a first optical fiber port inoptical communication with the first correcting element and operable tobe coupled to the proximal end of an optical fiber.
 11. The surgicalillumination apparatus of claim 10, wherein the first correcting elementcomprises a fresnel lens.
 12. The surgical illumination apparatus ofclaim 10, wherein the first correcting element comprises an axiconiclens.
 13. The surgical illumination apparatus of claim 12, wherein theaxiconic lens comprises a single-zone axicon.
 14. The surgicalillumination apparatus of claim 12, wherein the axiconic lens comprisesa multi-zone axicon.
 15. The surgical illumination apparatus of claim12, wherein the axiconic lens comprises a negative axicon.
 16. Thesurgical illumination apparatus of claim 12, wherein the illuminationsource comprises a xenon lamp.
 17. The surgical illumination apparatusof claim 16, further comprising an optical fiber coupled to the opticalfiber port having a diameter of less than or equal to the diameter of a25-gauge fiber.
 18. The surgical illumination apparatus of claim 10,wherein the first mirror or the second mirror remove infrared componentsof the optical beam.
 19. A method for shaping an optical beam foroptical coupling to an optical fiber, comprising: generating an opticalbeam using an illumination source; directing the optical beam to acorrecting element; reshaping the optical beam using the correctingelement to have a focal spot with a more Gaussian intensity distributionthan upstream of the correcting element; optically coupling the shapedoptical beam to an optical fiber; and directing the optical beam to asurgical site.
 20. The method of claim 19, wherein the correctingelement comprises a fresnel lens.
 21. The method of claim 19, whereinthe correcting element comprises an axiconic lens.
 22. The method ofclaim 21, wherein the axiconic lens comprises a single-zone axicon. 23.The method of claim 21, wherein the axiconic lens comprises a multi-zoneaxicon.
 24. The method of claim 21, wherein the axiconic lens comprisesa negative axicon.